19.10.1 Introduction
Under particular through-feed centerless grinding conditions, results presented by Koenig and Henn [1982] showed that the minimum cost per part was achieved at removal rates between 1 and 6 mm3/mm/s. Increasing or reducing removal rate from this range increased costs. Such results are useful for demonstrating an approach to optimization. In this section, a general approach to optimization is demonstrated.
The following analysis by Rowe and Ebbrell [2004] demonstrates how a systematic approach can allow many different factors to be taken into account leading to large increases in productivity and reductions in costs while maintaining quality levels. The analysis applies for repeated batch manufacture. Costs in grinding can often be reduced by increasing removal rate. However, this is not the only factor and it is necessary to take account of mean cycle time including dwell time for
spark-out and costs related to labor, the grinding machine, grinding wheels, dressing, and maintenance of required quality levels.
As demonstrated in Section 19.9, high wheel speeds allow removal rates to be increased while maintaining quality levels. However, high wheel speeds increase the cost of the grinding machine. Stiffer machines are required. More sophisticated equipment and techniques are required for fluid delivery, dressing, and spindle bearings. Special grinding wheels are required for high speeds and better machine guarding. It is, therefore, necessary to give consideration to costs and benefits of these various aspects. Advantages may be obtained by introducing superabrasive wheels to allow much higher wheels speeds and long redress life.
Redress life results were obtained in grinding between centers using smaller wheels to minimize wheel costs. However, the principles are generally applicable. Repeated batch manufacture is a situation where it is required to maximize production throughput and minimize process costs while achieving specified quality levels.
19.10.2 Cost Relationships
The following cost analysis takes account of labor cost, machine cost, and abrasive cost. Workpiece quality and redress life are related through the number of parts ground before roughness or roundness tolerance is exceeded.